Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Hot Rocks Survey. IV. Emission from LTT 3780 b Is Consistent with a Bare Rock

Allen, Natalie H. ; Espinoza, Néstor ; Diamond-Lowe, Hannah ; Mendonça, João M. ; Demory, Brice Olivier ; Gressier, Amélie ; Ih, Jegug ; Fortune, Mark ; August, Prune C. and Holmberg, Måns , et al. (2025) In Astronomical Journal 170(4).
Abstract

It is an open question whether small planets around M dwarfs are able to maintain atmospheres. The Hot Rocks Survey aims to address this question by observing nine rocky exoplanets orbiting M dwarfs with MIRI emission photometry to constrain the onset of atmospheres. In this paper, we present two MIRI F1500W (15 μm) eclipses of LTT 3780 b, an ultrashort-period super-Earth (P = 0.768 days, R = 1.325 R⊕, M = 2.46 M⊕) that receives 111× Earth’s instellation, the highest in the survey. We find a combined eclipse depth of 312 ± 38 ppm, which is consistent between different data reduction and analysis assumptions, bolstering our confidence in the eclipse detection. This eclipse depth is consistent with the thermal... (More)

It is an open question whether small planets around M dwarfs are able to maintain atmospheres. The Hot Rocks Survey aims to address this question by observing nine rocky exoplanets orbiting M dwarfs with MIRI emission photometry to constrain the onset of atmospheres. In this paper, we present two MIRI F1500W (15 μm) eclipses of LTT 3780 b, an ultrashort-period super-Earth (P = 0.768 days, R = 1.325 R⊕, M = 2.46 M⊕) that receives 111× Earth’s instellation, the highest in the survey. We find a combined eclipse depth of 312 ± 38 ppm, which is consistent between different data reduction and analysis assumptions, bolstering our confidence in the eclipse detection. This eclipse depth is consistent with the thermal emission from a bare rock surface, with a dayside temperature of T day = 114 3 − 99 + 104 K, 98% ± 9% of the maximum temperature predicted for a zero-albedo, zero heat redistribution blackbody. We are able to confidently rule out CO2-based atmospheres down to a 0.01 bar surface pressure to greater than 3σ (ruling out an approximately Mars-like atmosphere). We are unable to rule out a pure H2O 1 bar atmosphere, though we argue that this composition is unlikely on such a highly irradiated planet, nor O2 atmospheres due to the lack of features in the bandpass, though we can put constraints on CO2-mixture atmospheres. As a potential bare rock, we consider a variety of surface composition models, but are unable to distinguish between them. However, LTT 3780 b is an excellent target for follow-up JWST observations to determine its surface composition and rule out additional atmospheric compositions.

(Less)
Please use this url to cite or link to this publication:
author
; ; ; ; ; ; ; ; and , et al. (More)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; and (Less)
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Astronomical Journal
volume
170
issue
4
article number
240
publisher
IOP Publishing
external identifiers
  • scopus:105017163495
ISSN
0004-6256
DOI
10.3847/1538-3881/adfc51
language
English
LU publication?
yes
id
330a344a-85bb-4c31-972b-871261607604
date added to LUP
2025-11-26 11:34:16
date last changed
2025-11-26 11:35:06
@article{330a344a-85bb-4c31-972b-871261607604,
  abstract     = {{<p>It is an open question whether small planets around M dwarfs are able to maintain atmospheres. The Hot Rocks Survey aims to address this question by observing nine rocky exoplanets orbiting M dwarfs with MIRI emission photometry to constrain the onset of atmospheres. In this paper, we present two MIRI F1500W (15 μm) eclipses of LTT 3780 b, an ultrashort-period super-Earth (P = 0.768 days, R = 1.325 R<sub>⊕</sub>, M = 2.46 M<sub>⊕</sub>) that receives 111× Earth’s instellation, the highest in the survey. We find a combined eclipse depth of 312 ± 38 ppm, which is consistent between different data reduction and analysis assumptions, bolstering our confidence in the eclipse detection. This eclipse depth is consistent with the thermal emission from a bare rock surface, with a dayside temperature of T day = 114 3 − 99 + 104 K, 98% ± 9% of the maximum temperature predicted for a zero-albedo, zero heat redistribution blackbody. We are able to confidently rule out CO<sub>2</sub>-based atmospheres down to a 0.01 bar surface pressure to greater than 3σ (ruling out an approximately Mars-like atmosphere). We are unable to rule out a pure H<sub>2</sub>O 1 bar atmosphere, though we argue that this composition is unlikely on such a highly irradiated planet, nor O<sub>2</sub> atmospheres due to the lack of features in the bandpass, though we can put constraints on CO<sub>2</sub>-mixture atmospheres. As a potential bare rock, we consider a variety of surface composition models, but are unable to distinguish between them. However, LTT 3780 b is an excellent target for follow-up JWST observations to determine its surface composition and rule out additional atmospheric compositions.</p>}},
  author       = {{Allen, Natalie H. and Espinoza, Néstor and Diamond-Lowe, Hannah and Mendonça, João M. and Demory, Brice Olivier and Gressier, Amélie and Ih, Jegug and Fortune, Mark and August, Prune C. and Holmberg, Måns and Meier Valdés, Erik and Zgraggen, Merlin and Buchhave, Lars A. and Burgasser, Adam J. and Fisher, Chloe and Gibson, Neale P. and Heng, Kevin and Hoeijmakers, Jens and Kitzmann, Daniel and Prinoth, Bibiana and Rathcke, Alexander D. and Morris, Brett M.}},
  issn         = {{0004-6256}},
  language     = {{eng}},
  number       = {{4}},
  publisher    = {{IOP Publishing}},
  series       = {{Astronomical Journal}},
  title        = {{Hot Rocks Survey. IV. Emission from LTT 3780 b Is Consistent with a Bare Rock}},
  url          = {{http://dx.doi.org/10.3847/1538-3881/adfc51}},
  doi          = {{10.3847/1538-3881/adfc51}},
  volume       = {{170}},
  year         = {{2025}},
}